Among the problems encountered in designing these cells, there is that of storage before use or during long rest periods between discharges, as well as that of loss of capacity during slow-rate discharging. Of course, an air-depolarized cell must be accessible to air during discharge, but air must never come directly into contact with the negative electrode because this may cause a loss of usable capacity.
Various steps have therefore been taken to prevent air from oxidizing the negative active material. U.S. Pat. No. 3,840,406 discloses a negative electrode covered with a layer of electrolytic gel which protects it from the air contained in an expansion chamber provided in the upper portion of the cell to compensate for the increase in volume of the negative electrode during discharge. However, the oxygen in said space becomes dissolved in the electrolyte and comes into contact with the anode active material. It is therefore important that said space does not communicate with the outside, and steps have been taken to this effect in U.S. Pat. No. 4,214,044. These steps consist in limiting the space in consideration on the positive electrode side (and hence on the air intake side) by means of an air-tight wall.
However, it has been found that this disposition, although effective to some extent, is insufficient in some cases. Air entering through the immersed portion of the positive electrode can form pockets between the electrolyte and the wall of the positive electrode and is thus able to make cracks appear in the electrolytic gel. This phenomenon probably occurs because of the pressure drop caused in the expansion space above the electrolyte by the disappearance of the oxygen dissolved in the electrolyte and combined with the negative active material, or is due to variations in temperature or atmospheric pressure.
Preferred embodiments of the present invention remedy this drawback.